The microstructure fragmentation in iron tensile specimens deformed at room temperature and 600°C has been studied by means of EBSD. The aim of the research was to characterize and compare the patterns of fragmentation associated with the appearance and accumulation of deformation-induced high-angle boundaries (HABs). The microstructure was examined on the longitudinal section of necked specimens, in locations corresponding to various true strains from 0.5 to 1.6. It has been shown that a length of deformation-induced boundaries per unit area is characterized by rapid growth at small strains. With further straining, it ceases to grow in a low-angle interval of misorientations, whereas continues to grow in a high-angle interval. The accumulation of HABs occurs considerably faster during cold deformation, mainly through the formation of transition zones between grain-scale deformation bands.